The present invention concerns a procedure for rendering odourless the evil-smelling waste waters and waste gases generated in the cellulose industry. More specifically, the invention concerns a biofilter for carrying out the procedure disclosed in the Finnish Pat. No. 46,497.
In the above-mentioned Patent in the purification of waste waters and waste gases coniferous tree barking residues are utilized, through which the substances to be purified are conducted. The barking residue has been placed on trays permeable to liquid and gas and which have to support the barking residue layer in such manner that the liquids and gases can freely pass through the layer, however without any substance being permitted to run from the filtering layer and to follow along with the flowing liquid.
It was found, as realization of the invention was undertaken on a practical scale, that if the process is desired to have a sufficient capacity one is compelled to erect a comparatively large diameter structure of concrete or sheet steel, and this involves certain drawbacks. One of the major drawbacks is that the trays supporting the filtering layer and permeable to gas and liquid must be dimensioned to be comparatively strong and they must be heavily braced against the side walls. The result hereof is an expensive and massive construcion, because the structure has to be gas and liquid tight. Furthermore in view of best efficiency in the operation of the process, one has to provide for uniform distribution of liquid and gas and for removal of the purified liquid.
The aims of the invention have been achieved according to the invention in a simple way in that the filtering barking residue layer is placed in a depression made in the ground, whereby no concrete or sheet steel structure is required for side walls, instead of which the sides of the barking residue heap are lined with plastic fabric and upon the filtering layer a roof has been disposed so that the construction becomes liquid and gas tight.
The foregoing features and advantages of the present invention will become more apparent from a description of the invention in connection with the accompanying drawings and the characteristic features of the invention are covered in the appended claims.